U.S. patent application number 14/416288 was filed with the patent office on 2015-06-25 for method and arrangement for mobility procedures.
This patent application is currently assigned to Telefonaktiebolaget L M Ericsson (publ). The applicant listed for this patent is Telefonaktiebolaget L M Ericsson (publ). Invention is credited to Angelo Centonza, Mojgan Fadaki, Fredrik Gunnarsson, Gino Luca Masini, Gunnar Mildh, Oumer Teyeb, Stefan Wager.
Application Number | 20150181481 14/416288 |
Document ID | / |
Family ID | 48539192 |
Filed Date | 2015-06-25 |
United States Patent
Application |
20150181481 |
Kind Code |
A1 |
Masini; Gino Luca ; et
al. |
June 25, 2015 |
Method and Arrangement for Mobility Procedures
Abstract
Cooperating nodes, and methods therein, for mobility procedures
in a wireless communication system supporting UE groups. One of the
cooperating nodes is a base station being associated with a UE
group comprising UEs having correlated mobility related parameters.
The method in the base station comprises receiving, from a first UE
in the UE group, a mobility related parameter associated with the
first UE. The method further comprises determining whether to
initiate a mobility related procedure for a second UE in the UE
group based on the received mobility related parameter; and further
comprises initiating the mobility related procedure for the second
UE when it is determined that the mobility related procedure is to
be performed. Thereby, prediction and decisions related to mobility
events, e.g. handover events, for the second UE or for the whole
group may be performed e.g. before or without receiving any
mobility information related to the second UE, thereby enabling
early prediction and better preparation, which can lead to more
robust mobility procedures.
Inventors: |
Masini; Gino Luca;
(Stockholm, SE) ; Centonza; Angelo; (Winchester,
GB) ; Fadaki; Mojgan; (Solna, SE) ;
Gunnarsson; Fredrik; (Linkoping, SE) ; Mildh;
Gunnar; (Sollentuna, SE) ; Teyeb; Oumer;
(Solna, SE) ; Wager; Stefan; (Espoo, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Telefonaktiebolaget L M Ericsson (publ) |
Stockholm |
|
SE |
|
|
Assignee: |
Telefonaktiebolaget L M Ericsson
(publ)
|
Family ID: |
48539192 |
Appl. No.: |
14/416288 |
Filed: |
June 3, 2013 |
PCT Filed: |
June 3, 2013 |
PCT NO: |
PCT/EP2013/061369 |
371 Date: |
January 22, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61679253 |
Aug 3, 2012 |
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Current U.S.
Class: |
455/436 |
Current CPC
Class: |
H04W 36/0058 20180801;
H04W 36/0083 20130101; H04W 36/32 20130101; H04W 36/00835 20180801;
H04W 36/0055 20130101; H04W 36/0085 20180801 |
International
Class: |
H04W 36/00 20060101
H04W036/00 |
Claims
1-30. (canceled)
31. A method performed by a base station in a wireless
communication system, the base station being associated with a User
Equipment (UE) group comprising UEs having correlated mobility
related parameters, the method comprising: receiving, from a first
UE in the UE group, a mobility related parameter associated with
the first UE; determining whether to initiate a mobility related
procedure for a second UE in the UE group based on the received
mobility related parameter; initiating the mobility related
procedure for the second UE when it is determined that the mobility
related procedure is to be performed.
32. The method of claim 31, wherein the determining comprises
determining whether to initiate a mobility related procedure for
the first UE based on the received mobility related parameter and
applying the result on the second UE belonging to the same
group.
33. The method of claim 31, wherein the mobility related procedure
is a handover procedure.
34. The method of claim 31, wherein the initiating comprises
transmitting a handover request to a target network node.
35. The method of claim 31, wherein the mobility related parameter
is at least one of: a report of a measured signal strength at the
first UE; a report of a measurement on a signal received by the
first UE from a neighboring base station; information on the
geographical position of the first UE; a report of a measurement on
a signal received by the first UE from an access point in another
wireless communication system.
36. The method of claim 31: further comprising receiving a
respective mobility related parameter associated with a number of
other UEs in the UE group; wherein the initiating of the mobility
related procedure is further based on a received number of mobility
related parameters.
37. The method of claim 31, wherein the mobility related procedure
is initiated towards a cell, which cell is reported as being a
neighbor cell by the largest number of UEs in the UE group or which
cell is the strongest cell reported by a plurality of UEs in the UE
group.
38. The method of claim 31, wherein the mobility related procedure
is initiated for a plurality of UEs in the UE group, the plurality
comprising the second UE.
39. The method of claim 31, wherein the mobility related procedure
is initiated for the whole UE group.
40. The method of claim 31, wherein the initiating comprises using
a single mobility command for a plurality of UEs in the UE
group.
41. A method performed by a network node associated with a handover
of a plurality of User Equipment (UEs) in a UE group, the UE group
comprising UEs having correlated mobility related parameters, the
method comprising: receiving information indicating that the
plurality of UEs being subjected to the handover have connected to
a target node; transmitting a single path switch request or a
single modify bearer request for the plurality of UEs.
42. The method of claim 41, wherein the network node is the target
node to which the plurality of UEs is handed over.
43. A method performed by a first User Equipment (UE) comprised in
a UE group comprising UEs having correlated mobility related
parameters, the first UE having access to a first identifier
identifying the UE group in which the first UE is comprised, the
method comprising: receiving a broadcasted mobility related command
from a base station, the command comprising a second identifier,
identifying a UE group; determining, based on the first and second
identifier, whether the first UE belongs to the UE group identified
by the second identifier; responding to the received command when
it is determined that the first UE belongs to the UE group
identified by the second identifier.
44. The method of claim 43: wherein the first UE is further
associated with an identity within the UE group; wherein the
mobility related command further comprises a Cell Radio Network
Temporary Identifier (CRNT-I) assigned to a UE in the UE group
identified by the second identifier; further comprising
determining, when the first UE belongs to the UE group identified
by the second identifier, a CRNT-I assigned to the first UE based
on the identity within the UE group and the CRNT-I comprised in the
mobility related command.
45. A base station operable in a wireless communication system and
further operable to be associated with a User Equipment (UE) group
comprising UEs having correlated mobility related parameters, the
base station comprising: one or more processing circuits configured
to function as: a receiving circuit configured to receive, from a
first UE in the UE group, a mobility related parameter associated
with the first UE; a determining circuit configured to determine
whether to initiate a mobility related procedure for a second UE in
the UE group based on the received mobility related parameter; a
mobility control circuit configured to initiate the mobility
related procedure for the second UE when it is determined that the
mobility related procedure is to be performed.
46. The base station of claim 45, wherein the determining circuit
is configured to: determine whether to initiate the mobility
related procedure for the first UE based on the received mobility
related parameter; apply the result on the second UE belonging to
the same group.
47. The base station of claim 45, wherein the mobility related
procedure is a handover procedure.
48. The base station of claim 45, wherein mobility control circuit
configured to initiate the mobility related procedure by
transmitting a handover request to a target network node.
49. The base station of claim 45, wherein the mobility related
parameter is at least one of: a report of a measured signal
strength at the first UE; a report of a measurement on a signal
received by the first UE from a neighboring base station;
information on the geographical position of the first UE; a report
of a measurement on a signal received by the first UE from an
access point in another wireless communication system.
50. The base station of claim 45: wherein the base station is
further configured to receive a respective mobility related
parameter associated with a number of other UEs in the UE group;
wherein the mobility control circuit configured to initiate the
mobility related procedure further based on the received number of
mobility related parameters.
51. The base station of claim 45, wherein the mobility control
circuit configured to initiate the mobility related procedure
towards a cell, which cell is reported as being a neighbor cell by
the largest number of UEs in the UE group or which cell is the
strongest cell reported by a plurality of UEs in the UE group.
52. The base station of claim 45, wherein the mobility control
circuit configured to initiate the mobility related procedure for a
plurality of UEs in the UE group, the plurality comprising the
second UE.
53. The base station of claim 45, wherein the mobility control
circuit configured to initiate the mobility related procedure for
the whole UE group.
54. The base station of claim 45, wherein the mobility control
circuit configured to initiate the mobility related procedure using
a single mobility command for a plurality of UEs in the UE
group.
55. A network node operable to be associated with a handover of a
plurality of User Equipment (UEs) in a UE group, the UE group
comprising UEs having correlated mobility related parameters, the
network node comprising: one or more processing circuits configured
to function as: a receiving circuit configured to receive
information indicating that the plurality of UEs being subjected to
the handover have connected to a target node; a control circuit
configured to transmit a single path switch request or a single
modify bearer request for the plurality of the UEs in the UE group
being subjected to the handover.
56. The network node of claim 55, wherein the network node is the
target node to which the plurality of UEs is handed over.
57. A first User Equipment (UE) operable to be comprised in a UE
group comprising UEs having correlated mobility related parameters,
and to have access to a first identifier identifying the UE group
in which the first UE is comprised, the UE comprising: one or more
processing circuits configured to function as: a receiving circuit
configured to receive a broadcasted mobility related command from a
base station, the command comprising a second identifier,
identifying a UE group; a determining circuit configured to
determine, based on the first and second identifier, whether the UE
belongs to the UE group identified by the second identifier; and a
mobility response circuit configured to respond to the received
command when it is determined that the UE belongs to the UE group
identified by the second identifier.
58. The first UE of claim 27, further being operable to be
associated with an identity within the UE group, and wherein the
received mobility related command further comprises a Cell Radio
Network Temporary Identifier (CRNT-I) assigned to a UE in the UE
group identified by the second identifier; wherein the UE is
further configured to determine, when the first UE belongs to the
UE group identified by the second identifier, a CRNT-I, assigned to
the first UE, based on the identity within the UE group and the
CRNT-I comprised in the mobility related command.
59. A computer program product stored in a non-transitory computer
readable medium for controlling a base station in a wireless
communications system, the base station being associated with a
User Equipment (UE) group comprising UEs having correlated mobility
related parameters, the computer program product comprising
software instructions which, when run on one or more processing
circuits of the base station, cause the base station to: receive,
from a first UE in the UE group, a mobility related parameter
associated with the first UE; determine whether to initiate a
mobility related procedure for a second UE in the UE group based on
the received mobility related parameter; initiate the mobility
related procedure for the second UE when it is determined that the
mobility related procedure is to be performed.
60. A computer program product stored in a non-transitory computer
readable medium for controlling a network node in a wireless
communications system, the network node associated with a handover
of a plurality of User Equipment (UEs) in a UE group, the UE group
comprising UEs having correlated mobility related parameters, the
computer program product comprising software instructions which,
when run on one or more processing circuits of the network node,
cause the network node to: receive information indicating that the
plurality of UEs being subjected to the handover have connected to
a target node; transmit a single path switch request or a single
modify bearer request for the plurality of UEs.
61. A computer program product stored in a non-transitory computer
readable medium for controlling a first User Equipment (UE) in a
wireless communications system, the UE comprised in a UE group
comprising UEs having correlated mobility related parameters, the
first UE having access to a first identifier identifying the UE
group in which the first UE is comprised, the computer program
product comprising software instructions which, when run on one or
more processing circuits of the UE, cause the UE to: receive a
broadcasted mobility related command from a base station, the
command comprising a second identifier, identifying a UE group;
determine, based on the first and second identifier, whether the
first UE belongs to the UE group identified by the second
identifier; respond to the received command when it is determined
that the first UE belongs to the UE group identified by the second
identifier.
Description
TECHNICAL FIELD
[0001] The present application relates generally to mobility
procedures, and in particular to a method and arrangement for
managing user equipment (UE) groups.
BACKGROUND
[0002] In wireless communications systems, a UE produces
measurement reports to be provided to a base station (BS), such as
an eNB or NodeB. Such measurement reports may comprise e.g.
information related to a signal strength of signals received from
the BS and/or from neighbor cells. The UE sends its measurement
reports to the BS to allow the BS to make mobility, e.g. handover,
decisions for the UE. When a handover is needed, signaling between
a source BS and a target BS and resource allocation at the target
BS are carried out.
[0003] The more UEs there are in a wireless communication system
and the higher mobility of the UEs in the wireless communication
system, the more mobility related procedures and signaling must be
performed by the BSs in the system. When a BS is not able to handle
all mobility related procedures in a cell in time, this may result
e.g. in dropped calls or other negative user experiences for users
moving into or out of the cell.
SUMMARY
[0004] The present document discloses a method and apparatus for
improving handover performance for a group of UEs that are
identified as having similar, correlated, mobility patterns.
Similar mobility patterns may include geographical proximity and/or
similar speed and direction shared among a plurality of UEs. UEs
exhibiting similar mobility behaviors can be grouped together. The
use of such groups of UEs sharing common mobility patterns allows
prediction of and preparation for mobility events, e.g. handover
events, for the whole group or part of the group. Early prediction
and better preparation can lead to more robust mobility
procedures.
[0005] According to a first aspect, a method is provided, to be
performed by base station, such as an eNB, in a wireless
communication system. The base station is associated with a UE
group comprising UEs having correlated mobility related parameters.
The method comprises receiving, from a first UE in the UE group, a
mobility related parameter associated with the first UE. The method
further comprises determining whether to initiate a mobility
related procedure for a second UE in the UE group, based on the
received mobility related parameter. The method further comprises
initiating the mobility related procedure for the second UE when it
is determined that the mobility related procedure is to be
performed.
[0006] According to a second aspect, a method is provided, to be
performed by a network node associated with a handover of a
plurality of UEs in a UE group to a target node. The method
comprises receiving information indicating that the plurality of
UEs being subjected to the handover have connected to the target
node; and transmitting a single path switch request or a single
modify bearer request for the plurality of UEs.
[0007] According to a third aspect, a base station is provided,
which is operable in a wireless communication system. The base
station is adapted to perform the method according to the first
aspect above. The base station comprises a receiving unit, adapted
to receive, from a first UE in the UE group, a mobility related
parameter associated with the first UE. The base station further
comprises a determining unit, adapted to determine whether to
initiate a mobility related procedure for a second UE in the UE
group based on the received mobility related parameter; and further
comprises a mobility control unit, adapted to initiate the mobility
related procedure for the second UE when it is determined that the
mobility related procedure is to be performed.
[0008] According to a fourth aspect, a network node is provided,
which is operable in a communication system. The network node is
adapted to perform the method according to the second aspect. The
network node comprises a receiving unit, adapted to receive
information indicating that the plurality of UEs being subjected to
the handover have connected to a target node. The network node
further comprises a control unit, adapted to transmit a single path
switch request or a single modify bearer request for the plurality
of the UEs in the UE group being subjected to the handover.
[0009] According to a fifth aspect, a computer program is provided,
comprising computer readable code means, which when run in a
network node according to the third or fourth aspect causes the
network node to perform the method according to the first or second
aspect, respectively.
[0010] According to a sixth aspect, a computer program product is
provided, comprising a computer program according to the fifth
aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The solution disclosed herein will now be described in more
detail by means of exemplifying embodiments and with reference to
the accompanying drawings, in which:
[0012] FIGS. 1-3 are flow charts illustrating procedures, according
to exemplifying embodiments in different nodes.
[0013] FIG. 4 illustrates signaling flows in an intra MME/S-GW
handover event
[0014] FIG. 5 is a flowchart illustrating an exemplary process of
managing a UE mobility group.
[0015] FIG. 6 is a flowchart illustrating an exemplary process of
identifying a UE mobility group.
[0016] FIG. 7 illustrates an exemplary method of identifying mobile
terminals location areas.
[0017] FIGS. 8 and 9 are flow charts illustrating exemplifying
procedures according to exemplifying embodiments.
[0018] FIGS. 10-13 are block charts illustrating arrangements
according to exemplifying embodiments.
[0019] FIG. 14 illustrates an exemplary apparatus configured to
manage the handover of a UE mobility group as a group.
[0020] FIG. 15 illustrates an exemplary apparatus configured to
receive and process group handover commands.
[0021] FIG. 16 is a network diagram illustrating the logic
interfaces between radio access nodes and core nodes in an
exemplary wireless network.
[0022] FIG. 17 is a diagram illustrating an exemplary management
system in a communications network.
[0023] FIG. 18 illustrates a handover event triggered by signal
strength measurements of two neighboring cells.
[0024] FIG. 19 illustrates different messages used in an exemplary
random access procedure.
[0025] FIG. 20 illustrates an exemplary timing advance mechanism
used in a LTE system.
[0026] FIG. 21 illustrates two received signal strengths associated
with signals from different sectors.
DETAILED DESCRIPTION
[0027] In current wireless communications systems, UEs are usually
managed individually. Each mobility event of a UE is handled
independently from mobility events associated with other UEs. For
example, during a handover situation, a UE performs measurement
reports independently of other UEs. Each UE sends its measurement
reports to a base station (BS), such as an eNB or NodeB, to allow
the BS to make handover decisions for that particular UE. Signaling
between a source BS and a target BS and resource allocation at the
target BS are also carried out on a per UE basis.
[0028] Managing UEs individually during a handover entails that the
network individually evaluates the condition for each UE and
executes handovers for every terminal. If a large number of UEs are
moving as a group at a high speed, a large number of handovers may
need to be executed within a very short time period. This may lead
to delays in the execution of handovers and potentially failures
due to a high number of handovers, and lack of anticipated handover
preparation.
[0029] UEs are usually individually monitored. Current solutions
lack means to deduce common mobility behaviors shared among
different UEs from events or trend information monitored for each
individual.
[0030] Current mobility procedures do not rely on common mobility
behaviors shared by a plurality of UEs, and therefore handle
mobility events for each UE separately. There is a need for
enhanced mobility procedures that can take advantage of the common
mobility behaviors identified for a group of UEs. Methods and
apparatuses for enabling such enhanced mobility procedures are
provided by the herein suggested solution.
[0031] In the following paragraphs, different aspects of the
disclosed solution will be described in more detail with references
to certain embodiments of the disclosed solution and to
accompanying drawings. For purposes of explanation and not
limitation, specific details are set forth, such as particular
scenarios and techniques, in order to provide a thorough
understanding of the different embodiments. However, other
embodiments may depart from these specific details. Further
information on some of the mobility related parameters discussed
herein, and their use, can be found in an appendix to the detailed
description. It has been placed at the end of the detailed
description in order not to obscure the understanding of the herein
suggested solution.
[0032] Exemplifying embodiments of a method performed by a base
station, such as an eNB, in a wireless communication system will
now be described with reference to FIG. 1. The base station is
associated with a UE group comprising UEs having correlated
mobility related parameters. Such a UE group could also be denoted
e.g. a "UE mobility group" or "mobility group". The creation of
such a UE group is not the focus of this disclosure, but is
described in a related non-published application. The creation of
such a UE group will also be described further below.
[0033] FIG. 1, illustrates the method comprising receiving 101,
from a first UE in the UE group, a mobility related parameter
associated with the first UE. The method further comprises
determining 102 whether to initiate a mobility related procedure
for a second UE in the UE group, based on the received mobility
related parameter. The method further comprises initiating 103 the
mobility related procedure for the second UE when it is determined
that the mobility related procedure is to be performed.
[0034] The base station receives a mobility related parameter, or
information on said parameter, from a UE in the UE group. It is
assumed to be clearly defined which UEs that belong to the group,
so this is known to the base station. The mobility related
parameter may be a number of different parameters, which will be
further described below.
[0035] The determining of whether to initiate a mobility related
procedure for a second UE in the UE group is based on the received
mobility related parameter, which is associated with a first UE in
the UE group, which may appear illogical. However, this is a
special point of the method, that a conclusion may be drawn for a
second UE based on information related to another, first, UE. In
the prior art, all mobility decisions for a UE are based on
information from and about the UE itself. In this case, however, it
is based on information associated with another UE in the UE group.
This is possible due to the properties of the group, which will be
described further below.
[0036] Thus, when it is determined that the mobility related
procedure is to be initiated for the second UE, said mobility
related procedure is initiated for the second UE, in accordance
with a procedure therefore. Examples of mobility related procedures
will be given further below.
[0037] The method enables e.g. prediction of, and preparation for,
mobility related procedures for a UE, even when no, or
insufficient, information is received or retrieved from said UE.
The method enables making fast decisions.
[0038] The determining of whether to initiate a mobility related
procedure for a second UE may comprise determining whether to
initiate a mobility related procedure for the first UE based on the
received mobility related parameter, and applying the result on the
second UE, which belongs to the same UE group as the first UE.
[0039] The determining of whether to initiate a mobility related
procedure for the first UE may be performed according to known
methods therefore. It may for example be determined whether the
first UE receives a stronger signal from a neighbor base station
than from the serving base station, and whether a received signal
from the serving base station is strong enough according to
standardized rules therefore. Based on the properties of the UE
group, it may be assumed that since the first UE is in need of, or
would benefit from, a certain mobility related procedure, the
second UE is in need of, or would benefit from, the same mobility
related procedure as the first UE. The mobility related procedure
may be related e.g. to load sharing, in form of handing over a
group of UEs to an adjacent cell, which has more available capacity
than a serving cell.
[0040] The determining of whether or not to initiate a mobility
related procedure for the first UE may be performed in accordance
with an existing procedure which is already performed in a wireless
system of today. However, due to that the first and the second UE
belong to the same UE group, having a correlated mobility pattern,
the decision may be extended to apply for the second UE. The
mobility related procedure may be initiated also for the first UE,
or, for a subset of the UE group or for the whole UE group,
depending on how e.g. a set of rules therefore is configured.
[0041] The mobility related procedure may be e.g. a handover
preparation procedure or a handover procedure. A handover
preparation procedure may be initiated towards more than one target
node, and does not necessarily imply that a handover, in fact, will
be performed towards the target node. However, a handover
preparation procedure may be regarded as a part of a handover
procedure. As previously described, e.g. a handover preparation
procedure may be initiated for the second UE, when the mobility
related parameter associated with the first UE is indicative of
that a handover would be beneficial. This implies that mobility
decisions may be taken, e.g. for the whole group, as soon as
mobility information related to a first UE of the group is
received. Thereby, lots of signaling and time may be saved e.g. by
not requesting mobility related parameters from the rest of the UEs
in the group.
[0042] The initiating of a mobility related procedure may comprise
transmitting a handover request to a target network node, which is
also illustrated in FIG. 4. FIG. 4 will be described in more detail
further below.
[0043] The mobility related parameter may be one or more of: a
report of a measured signal strength at the first UE; a report of a
measurement on a signal received by the first UE from a neighboring
base station; information on the geographical position of the first
UE; and, a report of a measurement on a signal received by the
first UE from an access point in another wireless communication
system.
[0044] The report of a measured signal may be an indication e.g. of
a Reference Signal Received Power (RSRP) or Reference Signal
Received Quality (RSRQ). The UE may have performed measurements on
signals received from the serving base station or from a
neighboring base station in the wireless communication system in
which the base station and UE operates, or, from an access point or
base station in another wireless communication system, e.g. to
which the UE could be handed over. These measurements may then be
reported to the base station, which may make mobility related
decisions based on the reports. Information on the UE position may
be used to determine e.g. the position of the UE in relation to a
number of known neighboring base stations or known sources of
interference. Information on differences in geographical position
between two points in time may also be used for determining whether
the UE is heading towards a neighboring base station, and with
which velocity. For example, it may be determined based on one or
more of the mobility related parameters mentioned above whether a
UE in the UE group, or the whole UE group, is moving towards a cell
border, and it may further be predicted if and when the UE or UE
group will need to be handed over to a neighboring cell, e.g. the
one it approaches.
[0045] Further information on UE measurements may be found in the
appendix to the detailed description further below.
[0046] Further, a respective mobility related parameter associated
with a number of other UEs in the UE group may be received by the
base station. In such a case, the initiating of the mobility
related procedure may be based also on said received number of
mobility related parameters.
[0047] The mobility related parameters (e.g. one per UE) associated
with the number of other UEs in the UE group is received in
addition to the mobility related parameter associated with the
first UE. The decision is thus made based on the mobility related
parameter associated with the first UE and the mobility related
parameters associated with the number of UEs in the UE group. By
"number of UEs" is meant one or more UEs. For example, the mobility
related parameter associated with the number of UEs may relate to
the received signal strength of neighboring base stations or
cells.
[0048] The mobility related procedure may be initiated towards a
cell, which cell is reported as being a neighbor cell by the
largest number of UEs in the UE group (from which mobility related
parameters have been received) or which cell is the strongest cell
reported by a plurality of UEs in the UE group.
[0049] For example, the base station may wait for several UEs in
the same group to report strong neighbors before initiating a
preparation for handover. The base station may then perform a
handover preparation for one, some, or all UEs in the UE group
towards a subset of the reported neighbors. The subset may be
selected based on different criteria, such as the ones listed above
or below. For example, the base station can select as candidate
target nodes for handover of the one or more UEs: The cell(s)
reported by most UEs in the group; the strongest cell(s) reported
by all or some of the UEs in the group; or a combination of the
preceding two.
[0050] The mobility related procedure may be initiated for more UEs
than the second UE mentioned above. The mobility related procedure
may be initiated for a plurality of UEs in the UE group, said
plurality comprising the second UE. The mobility related procedure
may e.g. be initiated for the whole UE group based on the mobility
related parameter associated with the first UE.
[0051] The initiating of the mobility related procedure may
comprise use of a single mobility command for a plurality of UEs in
the UE group. That is, instead of sending one mobility command for
each UE which is to be e.g. handed over, i.e. a plurality of
mobility commands, a single mobility command is used, which
indicates the plurality of UEs for which a mobility related
procedure is initiated. This is an advantage, since it saves e.g. a
lot of signaling associated with the mobility related procedure,
and thus a lot of capacity and time, which would otherwise have
been spent on sending, receiving, interpreting and processing the
more extensive signaling.
[0052] Embodiments herein also relate to a method performed by a
network node associated with a handover of a plurality of UEs in a
UE group to a target node. The UE group is the same type of UE
group as described above, and comprises UEs having correlated
mobility related parameters. Such a method will now be described
with reference to FIG. 2. FIG. 2 illustrates the method comprising
receiving 201 information indicating that the plurality of UEs
being subjected to the handover have connected to the target node;
and transmitting 202 a single path switch request or a single
modify bearer request for the plurality of UEs.
[0053] The network node may be the target node, to which the
plurality of UEs have connected/been handed over, or, the network
node could be an MME (Mobility Management Entity). That is the
reason for the transmitting of either a single path switch request
or of a single modify bearer request. In case the network node is a
base station, i.e. the target node, it will transmit a single path
switch request to an MME. In case the network node is an MME, it
will transmit a single modify bearer request e.g. to a serving
gateway. This is also illustrated in FIG. 4.
[0054] In prior art, one such message, i.e. path switch request or
modify bearer request, would have been transmitted for each of the
plurality of UEs. By sending one single message identifying a
plurality of UEs in a UE group, signaling is saved, which imply
that time and resources are saved.
[0055] The received information indicating that the plurality of
UEs being subjected to a handover have connected to a target node
will also be different depending on whether the node is a base
station or an MME. When the network node is a base station (the
target node) the information may be an RRC message received from
one or all of the plurality of UEs. The RRC message may be a
so-called RRC Connection Reconfiguration Complete message, which is
also illustrated in FIG. 4. When the network node is an MME, the
information may be e.g. a message received from the target base
station or the source base station.
[0056] Which type of information and signaling that is received may
depend on whether there is an X2 interface configured for the
source and target base stations. The nodes and messages described
above are mostly denoted with LTE terminology. However, the herein
suggested solution could also be applied in other types of
communication systems where nodes and signaling may be denoted
differently.
[0057] Embodiments herein also relate to a method performed by a
UE, below denoted a first UE, comprised in a UE group as the one
described above, comprising UEs having correlated mobility related
parameters. The first UE is having access to a first identifier,
identifying the UE group in which the first UE is comprised. By
"having access to" is meant that the UE has been informed of to
which UE group it belongs. This could have been indicated to the UE
e.g. by the network node creating the UE group or refining the UE
group, e.g. upon including the UE in the group. For example, a
serving base station could signal a UE group identifier to the UE,
which could be stored in a memory in the UE. This UE group
identifier could thus be the first identifier mentioned above.
[0058] Such a method performed by a UE will now be described with
reference to FIG. 3. FIG. 3 illustrates the method comprising
receiving 301 a broadcasted mobility related command from a base
station, said command comprising a second identifier, identifying a
UE group The method further comprises determining 302, based on the
first and second identifier, whether the first UE belongs to the UE
group identified by the second identifier. The method further
comprises responding 303 to the received command when it is
determined that the first UE belongs to the UE group identified by
the second identifier.
[0059] The mobility related command may be broadcasted from a
serving base station or a target base station. The mobility related
command may be related to handover, and be e.g. an RRC Connection
Reconfiguration message. Such a command may herein be denoted e.g.
"group handover command". By "target base station" may be
understood a base station serving the cell indicated as target cell
in the mobility related command. The command comprises a second
identifier, identifying a UE group, and the command is transmitted
in order to trigger a mobility related procedure for a plurality of
UEs. That is, the command is transmitted in order to trigger a
concerned plurality of UEs, namely UEs belonging to the identified
UE group, to take action in accordance with the mobility related
command. The first UE receives the broadcasted mobility related
command, and thus receives the second identifier.
[0060] The second identifier may be any type of group ID, e.g. a
numerical sequence. This requires that such a group ID has been
assigned to the group e.g. when the group was created. It further
requires that the UE has been informed of that it belongs to a
group, e.g. by being provided with the group ID. Alternatively or
in addition, the UE could have been assigned a group membership ID
comprising e.g. the group ID and an index indicating a
"group-member-number". When the first UE receives the second
identifier, and this is a group ID, it may compare the second
identifier to the first identifier, and determine whether there is
a match, e.g. that the same numerical sequence, e.g. of a
predetermined length in a predetermined position, is comprised both
in the first and second identifier, or, that the first and second
identifier consists of the same numerical sequence. For example, it
could be determined whether a group ID-part of the first identifier
corresponds to the group ID indicated by the second identifier.
When it is determined that there is a match, it may be determined
that the first UE belongs to the UE group which is identified by
the second identifier, and it may thus be concluded that the
mobility related command is intended also for the first UE.
[0061] The second identifier could alternatively identify a second
UE, representing the UE group. The first UE should then determine
whether it belongs to the same UE group as the identified second
UE. For example, the first UE may have received information on
which UEs that are comprised in the same UE group, e.g. in form of
a list or record connecting a set of UEs, by some type of
identifiers, to a UE group. The first UE may thus, by determining
e.g. that a certain numerical or alphabetical relation is at hand
between the first and second identifier, conclude that it belongs
to the UE group represented by the identifier of the second UE.
[0062] That the first UE "responds to the received command" means
that the first UE takes action as if the received mobility related
command had been an ordinary mobility related command intended e.g.
only for the first UE. If the command is related to handover, the
first UE should take the action necessary for being handed over to
a target cell which would also be identified in the handover
command.
[0063] The method described above enables the (first) UE to respond
to group mobility commands, even when it is not, as a UE
individual, explicitly addressed by the mobility command. Thereby
signaling may be saved, since one group command may be sent by a
serving or target base station instead of a number of commands,
e.g. one for each member of the group.
[0064] As previously mentioned, the first UE may be associated with
an identity, e.g. a sequence number, within the UE group. Further,
the mobility related command may comprise a CRNT-I assigned to a UE
in the UE group identified by the second identifier. When the first
UE belongs to the UE group identified by the second identifier, the
first UE may determine a CRNT-I, which has been assigned to it (to
the first UE), based on the identity within the UE group and the
CRNT-I comprised in the mobility related command. That is, the
CRNT-I assigned to the first UE, e.g. by a target base station, is
implicitly signaled to the first UE by the signaling of a CRNT-I of
another UE in the UE group, e.g. the UE having group membership
number "1". If the first UE then has group membership number "2",
it could derive its CRNT-I based on this information if the CRNT-Is
have been assigned according to a set of rules, and the first UE
has been instructed at some point on how to derive the CRNT-I. The
above saves explicit signaling of CRNT-Is, e.g. a t handover. This
will be described in more detail further below.
[0065] Herein, a method is disclosed, which is suitable for
managing UEs as a mobility group to optimize network performance.
The method, which may be implemented in different embodiments,
enables predicting an impending handover for a UE mobility group;
identifying a target node and a target cell associated with the
target node and affected UEs based on the impending handover;
preparing the target cell for the impending handover; and managing
the affected UEs as a group during the handover.
[0066] The method may comprise determining one or more mobility
measurements associated with a UE mobility group and predicting the
impending handover based on the mobility measurements. An impending
handover may also be predicted based load balancing between two
eNBs.
[0067] The one or more mobility measurements may include
measurement reports received from a subset of the UEs belonging to
the UE mobility group. When measurement report(s) from a subset of
the UEs belonging to the same group indicate a possible target eNB
or several possible target eNBs for handover, the target eNB(s) can
be prepared for the handover of the whole group, without waiting
for the measurement reports from all the UEs. This provides more
time for the source eNB to complete more handovers and reduces the
risk of handover failures, especially in cases in which many UEs
are traveling together, e.g., on board a high-speed train. This
also gives more time for the target eNB(s) to allocate the
resources required for the UE mobility group.
[0068] A group handover command may be issued collectively by an
eNB to all UEs in the group at the same time, saving significantly
on the required signaling.
[0069] Further, the common UE position and/or trajectory
information of a UE mobility group may be used to predict a
handover event and the likely target eNB(s) and target cell(s) for
the handover event. In anticipation of the handover event,
preparation for the handover of the entire group can be performed
in the cell(s) of the target eNB(s) that has been determined as
likely to receive the incoming UE group. This can significantly
reduce the amount of handover preparation, reduce handover
failures, and enable a more precise resource allocation at the
target eNB(s).
[0070] A single path switch command containing the information for
the entire group can be sent by a target eNB after a handover.
Accordingly, a single modify bearer request containing information
for the entire group may be sent by an MME.
[0071] A list of UEs included in a UE group may be signaled to the
MME (Mobility Management Entity) so that the whole group can be
tracked between handovers.
[0072] FIG. 5 is a flow chart illustrating an exemplary procedure
for handling a group handover. First an impending handover for a UE
mobility group is predicted 501, based on, e.g. one or more
mobility measurements or load balancing need of a serving eNB. Then
based on the impending handover, the possible target node and
target cell can be determined 502. Also the affected UEs to be
handed over to the target cell can be determined as well. The
target cell is then prepared 503 for the impending handover and the
handover of the affected UEs is managed 504 as a group.
[0073] In the present disclosure, methods and techniques are
disclosed for performing handover procedures for a UE group by
relying on the common mobility behaviors of UEs belonging to a UE
group. UEs belonging to an identified UE group can be managed as a
group during handover, resource allocation, or other management
activities. Managing multiple UEs as a group can save signaling
resources, reduce operation time, and improve performance.
[0074] In the present disclosure, an LTE system is used as the
exemplary radio access technology. However, the embodiments and
techniques disclosed herein are equally applicable to other radio
access technologies. In the present disclosure, the term UE and the
term mobile terminal may be used interchangeably. Further, the term
eNB and the term base station may be used interchangeably.
[0075] Below, the grouping of UEs into UE groups based on their
correlated mobility characteristics will be described with
reference to FIGS. 6 and 7
[0076] FIG. 6 is a flowchart describing an exemplary method of
classifying and grouping of UEs based on trend information.
Examples of trend information includes radio signal strength and
quality measurements, time alignment measurement, time difference
measurements from the UE, as well as channel sounding, random
access, time alignment measurements from the eNB. The trend
information can also be a velocity estimate as in the case of a
Doppler estimator in the eNB, or by comparing the rate of change of
measurements associated to two or more time instants.
[0077] Two exemplary criteria for grouping of UEs into the same
Mobility Group are the timing advance commands and the received
signal strength. Other criteria can be used e.g. to refine a UE
group already formed.
[0078] The method illustrated in FIG. 6 allows grouping of UEs
based on whether they are moving in a similar mobility pattern,
i.e. with similar speed, according to similar trajectories and in
the proximity of each other. With the possibility of such grouping
the serving base station can apply optimized mobility policies to
all the UEs forming the Mobility Group. For example, the serving
eNB may be able to predict and prepare for a handover event for the
UEs belonging to the Mobility Group. The method therefore helps
optimizing UE mobility performance and reduces mobility failures,
e.g., handover failures.
[0079] In FIG. 6, trend information associated with a first UE or a
group of UEs are first determined 601. The trend information
associated with a first UE or group of UEs is compared 602 to the
trend information associated with other UEs or groups of UEs. If
the trend information of a first UE or group of UEs is considered
related to the trend information of one or more UEs in a group, the
first UE or the group of UEs is associated 603 with (to) the
group.
[0080] FIG. 7 illustrates an exemplary method for identifying a UE
mobility group based on trend information comprises determining
trend information for a first UE or for each UE in a first group of
UEs; comparing the trend information of the first UE or the first
group of UEs with trend information of a second UE or a second
group of UEs; determining whether the trend information of the
first UE or the first group of UEs is related to the trend
information of the second UE or the second group of UEs based on a
first criterion; and if related, associating the first UE or the
first group of UE with the second UE or the second group of UEs to
form a UE mobility group.
[0081] An eNB may monitor the timing-advance commands or parameters
contained in the commands sent to all served UEs via MAC layer over
the DL-SCH channel. For example, the parameter monitored may be the
Timing Advance Command MAC control element, as specified in TS
36.321v10.5.0.
[0082] The Timing Advance Command MAC control element is used to
control the amount of timing adjustment that a UE has to apply in
UL for the PUCCH/PUSCH/SRS of the primary cell. Its value mainly
depends on the distance of the UE from the eNB and it is expressed
in multiples of 16 T.sub.s, where T.sub.s=1/(15000.times.2048)
seconds is the basic time unit. The index denoting the Timing
Advance Command MAC control element is constituted by an index
value TA (0, 1, 2 . . . 63), namely the index is 6 bits long.
However, it should be pointed out that Timing Advance commands can
also be sent as part of RACH access procedures, but in this case
the length of the index value TA is 11 bits, i.e. TA=(0, 1, 2, . .
. , 1282).
[0083] As shown in FIG. 7, mobile terminals receiving same or
similar Timing Advance Command MAC control elements, are either
equidistant from the eNB or within an area limited by a maximum and
minimum distance from the eNB. In FIG. 7, it is shown how mobile
terminals with timing advance setting within a certain range can be
located within an area delimited by a maximum and minimum distance
from the eNB. If the range of timing advance parameters considered
is narrow enough, it is possible to identify mobile terminals that
are almost equal distance from the eNB, depending on the errors to
which the timing alignment is subject and on particular multipath
conditions.
[0084] As mentioned above, timing advance commands can be sent as
part of dedicated MAC procedures while the UE is in RRC_Connected
state. Alternatively, they can be sent as part of the RACH access
procedures when the UE is attempting to move from RRC_Idle to
RRC_Connected state or when a UE is in a handover.
[0085] In the former case, the eNB would need to monitor the Timing
Advance Command MAC control element provided to UEs in connected
mode to derive similarities in the timing advance settings of
served UEs. In the latter case, the eNB would have to monitor Idle
to Active transitions or incoming handovers and in particular RACH
access procedures, in order to identify the timing advance setting
provided to the UE during such procedures and to derive similarity
with timing advance settings of other UEs.
[0086] However, using only timing advance settings is not
sufficient to identify a UE Mobility Group, namely a group of UEs
moving together. As shown in FIG. 7, UEs configured with timing
advance values within a certain range may be moving in completely
different directions and cannot necessarily be grouped together for
the purposes of applying shared mobility policies. Therefore a
second mechanism, e.g., based on detected cell signals, is needed
in order to properly identify a Mobility Group.
[0087] The serving eNB may monitor the UEs configured within a
certain range of timing alignment indices and tracks their received
served cell RSRP values and the RSRP values of each UE's monitored
neighbor cell. The signal strength monitored may belong to the same
radio access technology as the serving base station within the same
or different frequencies, or belong to different radio access
technologies than that used by the serving base station. For
example, the serving base station may be an LTE system, but the
monitored inter RAT signals may be from GSM or WCDMA cells. As
shown in FIG. 7, the trend information deduced from the monitored
serving and neighbor cells' RSRP will be similar within the same
Mobility Group, regardless whether the serving cell and the
neighbor cells are using the same radio access technologies.
[0088] As part of the RSRP monitoring the eNB could monitor the
following parameters in order to identify a Mobility Group of UEs
moving in a similar mobility pattern: [0089] Neighbor Cell Global
Identities and/or Physical Cell Identity of cells for which RSRP is
reported (or equivalent parameters for other RATs besides LTE, e.g.
Cell Global Identities and/or scrambling code of UTRAN cells for
which RSCP is reported). [0090] Gradient of variation of received
signal strength measurements (e.g. RSRP for LTE, RSCP for WCDMA)
from each UE and for each reported cell. [0091] Absolute values of
received signal strength measurements (e.g. RSRP for LTE, RSCP for
WCDMA) reported by each UE for each monitored cell within a given
time window.
[0092] Once the eNB has monitored timing advance settings e.g. for
each served UE and RSRP related characteristics for those UEs with
similar timing advance, the eNB will be able to identify the UEs
that are moving in a similar way, e.g., because located in the same
vehicle or following the same route at the same speed, and to group
them together in a Mobility Group.
[0093] The Mobility Group detected can be identified with a
Mobility Group ID assigned to the group. The eNB may decide to
apply the same or similar mobility policies to all UEs identified
under such a Mobility Group. This will be further described later
below.
[0094] The serving eNB may use other support information in
conjunction with or instead of Timing Alignment or RSRP. Different
parameters may be used alone or in combination to create and/or
refine the selection of UEs grouped in a Mobility Group. For
example, when a UE group has been identified according to the
timing advance mechanism and/or RSRP mechanism described above, one
or more of the following could be used to validate and/or refine
the list of UEs in the Mobility Group: [0095] Correlation of UE
History Information IE (see TS 36.413) received for handovers of
UEs of the same group. Namely to compare the time the UE History
Information IE was received for each UE (corresponding to the
completion of handover preparation for that UE), the list of cells
in this IE and the permanence time in each cell for each UE
provisionally included in a Mobility Group. If the correlation
matches, the UE is proven to be appropriately included in the
Mobility Group. For example, with respect to FIG. 7 all UEs in
Mobility Group n will be handed over from cell 1 to, e.g., cell 2
within a certain time window. Within such window eNB2 will receive
the UE History Information IE for each UE in the group. Further,
for each of these UEs the permanence time in Cell 1 will be similar
and the cells visited before cell 1 will also be similar. [0096]
Doppler estimation: the serving eNB may decide to trigger Doppler
estimation for some or all of the UEs initially included in the
Mobility Group. Such Doppler estimation will lead to calculation of
the frequency f.sub.r and eventually to the velocity of the UE for
which the calculation is performed. [0097] If the velocity of the
UEs for which a Doppler estimation is performed appear to be the
same or within given boundaries, the UEs are more likely to be
moving in a similar mobility pattern and should be kept in the same
Mobility Group. UEs with velocities that are outside the given
boundaries should be removed from the Mobility Group. [0098]
Monitoring of other Radio Access Technologies: upon receiving a new
indication over RRC, from the serving eNB to the UEs, that the UEs
have been included in a Mobility Group with given Mobility Group
ID, the UE may also be configured, or autonomously decide, to
monitor other available radio access technologies in the
neighborhood. [0099] This may lead to detection of, e.g., WiFi
cells or other types of radio signals by a UE belonging to a
mobility group. The UE may report such detection to the eNB. The
eNB, or the node in charge of managing mobility groups, can
therefore check whether the radio access technologies and signals
reported by the UEs in the Mobility Group are the same or similar.
If not the same, the eNB, or the node in charge of managing
mobility groups, may decide to move out of the Mobility Group those
UEs that have reported detection of different radio access
technologies or signals.
[0100] For example, in order to validate a Mobility group, a
serving eNB, or a node in charge of managing mobility groups, may
receive, from other network nodes such as the OAM system, an
indication of other radio access technologies monitored by the UEs.
Such information may be passed to the eNB, or the node in charge of
managing mobility groups, if the system is so configured that
measurements on other radio access networks are collected by a
centralized node in the network and are then passed to the serving
eNB, or the node in charge of managing mobility groups. Such
information can be used to validate whether UEs are appropriately
allocated to a Mobility Group. [0101] Positioning information: if
location information such as GPS location or any information
derived from the techniques described in section 1.6 is available
to the serving eNB, or the node in charge of managing mobility
groups, for some or all of the UEs included in the Mobility Group,
the eNB may check whether such information provided by each of the
UEs is sufficiently similar. Those UEs showing discrepancies in
their location with respect to other UEs in the Mobility Group may
be removed from the Mobility Group. [0102] Location information may
also be used by the serving eNB, or the node in charge of managing
mobility groups, to deduce the overall mobility patterns of the
Mobility Group. Namely, if it has been validated that all the UEs
in the Mobility Group are moving according to the same trends and
if only some of the UEs in the Mobility Group can provide location
information, the eNB, or the node in charge of managing mobility
groups, may assume the location information provided by a few UEs
as representing the mobility trend of the whole group. This might
help in applying more accurate and optimized mobility policies to
the Mobility Group. [0103] Angle of Arrival: If an estimate of the
angle of arrival in a new target cell can be performed for some or
all the UEs in a mobility group or for UEs not included in a
mobility group, this information can be used to either validate the
correctness of UE inclusion in or exclusion from a mobility
group.
[0104] Whenever the time advance criteria or cell signal strength
criteria are not met and/or when some or all of the criteria
specified above are not met, i.e. the information gathered for one
or more UEs via some or all of the above mentioned techniques do
not show any correlation, the eNB, or the node in charge of
managing mobility groups, may decide to remove the UE or those UEs
from the Mobility Group.
[0105] Thereby, the description of the related technique of
identifying and creating UE groups is completed. Below, the
managing of mobility related procedures in association with such UE
groups will be further discussed.
[0106] In the above sections, it is disclosed that a group of UEs
moving in a similar fashion can be identified, monitored and
updated. Once it has been determined that a number of UEs display
certain trends in terms of radio signal strength and quality
measurements, time alignment measurements, time difference
measurements among UEs as well as channel sounding, random access,
time alignment measurements from the eNBs, and that such UEs have
been classified as a UE group, such a UE group can be treated as if
it was a single UE. The identified mobility group may be labeled
with a Mobility Group ID, namely an identifier of the mobility
group. The multiple UEs in a mobility group can be collectively
handled during a handover. For instance, measurement reports from a
subset of UEs can be used to prepare handover for the entire group.
Collectively handling a handover for a UE mobility group may
further comprise issuing a group handover command to all UEs in the
group, preparing handover only to a subset of reported neighbors,
and/or issuing a single path switch request.
Using a Measurement Report from a Subset of UEs to Prepare Handover
for the Whole Group
[0107] In this exemplifying embodiment, a subset of one or more UEs
(henceforth referred to as "early UEs") that belong to a previously
identified UE mobility group send measurement reports to the
serving eNB. In the measurement reports, one or more neighbor cells
may be identified. The measurement reports from a subset of UEs can
be used to initiate the handover of all the UEs within the group
without necessarily waiting for measurement reports from each and
every UE within the group.
[0108] All the UEs in a mobility group demonstrate similar mobility
behavior relative to the network. For example, they may travel in
the same direction and at the same speed or be in the same position
roughly at the same time. Their relative position with respect to
each other may remain roughly the same on average. The eNB can
assume that every UE in the group will encounter the same mobility
events as the early UEs. The mobility event as experienced by each
UE may happen at different times, according to the UEs' different
positions and/or the differences in their RF performance.
[0109] Under this assumption, all the other UEs that are within the
same group as the early UEs but have not sent measurement reports
(henceforth referred to as "late UEs") are expected to send very
similar, if not identical, measurement reports. The eNB can
initiate a single or multiple HANDOVER PREPARATION procedures
towards the neighbor cell(s) in a target eNB reported by the early
UEs, for all the UEs in the same group. It shall be noted that
existing handover preparation procedures over the X2 interface or
over the S1 interface may be used for each UE as currently
specified in TS36.413 and TS36.423. For WCDMA such procedures may
be over the lu or lur interface per standard 25.413 and 25.423.
Therefore, the handover preparation procedure can be started for
all UEs that belong to the same Mobility Group without waiting for
measurement reports from every UE indicating that the handover
conditions are fulfilled.
[0110] A different approach to achieve handover preparation for all
UEs in the group is to use a single handover preparation signaling
for the whole group of UEs. In some embodiments, for an S1 handover
in a LTE system, there may be a single message for S1:HANDOVER
REQUIRED, S1:HANDOVER REQUEST, S1: HANDOVER REQUEST ACKNOWLEDGE and
S1: HANDOVER COMMAND. Similarly, for X2 handovers, a single X2:
HANDOVER REQUEST and X2: HANDOVER REQUEST ACKNOWLEDGE messages are
used for all the UEs that belong to the same mobility group. In
order to allow a single preparation for the whole group, a number
of approaches may be followed: [0111] 1) For core network based
mobility, UE specific information for all the UEs within the
mobility group can be listed in the Source to Target Transparent
Container. This per UE information includes, but is not limited to,
Radio Access Bearer information included in the RAB TrCH Mapping IE
for WCDMA and in the E-RABs Information List IE for LTE. This
information may also include a collective UE History Information IE
for all the UEs in the mobility group, where such IE is derived
from averaging the information in the UE History Information IE for
all the UEs in the mobility group. [0112] 2) Still for core network
based mobility and for the UEs whose bearer information has not
been included in the RAB TrCH Mapping IE for WCDMA or in the E-RABs
Information List IE for LTE, UE specific bearer and history
information can be included in the RRC Container IE present in the
Source To Target Transparent Container IE [0113] 3) For X2 or lur
based mobility and on top of the extra information included in the
Source To Target Transparent Container IE as described in bullet 1)
and 2), UE specific information for all or some of the UEs in the
mobility group can be included in the RABs To Be Setup List IE in
the RANAP ENHANCED INFORMATION REQUEST message for WCDMA and in the
UE Context Information IE container in the X2: HANDOVER REQUEST for
LTE. In the latter LTE case, the information regarding the UE
context of all or some of the UEs in the mobility group may also be
included in the RRC Context IE within the X2: HANDOVER REQUEST
message, possibly without any further additions to currently
standardized IEs.
[0114] An exemplary procedure is illustrated in FIG. 8. First, a UE
reports 801 strong neighbors to its serving eNB. The eNB checks 801
whether the UE is a member of a mobility group. If no, the eNB
proceeds with HANDOVER PREPARATION 803 for this UE only. If yes,
the eNB proceeds with HANDOVER PREPARATION 804 for all UEs in the
group, for a handover to the set of strong neighbors reported by
the UE.
[0115] In the case of sending only a single Handover request to all
of the UEs in the group, the HANDOVER REQUEST ACKNOWLEDGEMENT has
to contain the information regarding the group of UEs and their
bearers. The target includes a list of the new and old UE X2AP IDs
of all the UEs involved in the handover (in the case of X2
handover) or the MME UE S1 AP ID and eNB UE S1AP IDs of all the UEs
(in the case of S1 handover). The lists of admitted and
not-admitted bearers of all UEs may also be included in the E-RABs
admitted and E-RABs not-admitted lists, respectively. Apart from
that, the handover command to be sent to each UE is included in the
"Target eNB to Source eNB Transparent Container" IE in the case of
an X2 handover and "Target to Source Transparent Container" in an
S1 handover. If, as will be discussed in the next section, a
handover command is to be sent to all UEs in a broadcast fashion,
only one entry in the transparent container may be sufficient.
[0116] The triggering conditions set for a group handover can be
different from those set for individual handovers. For example, UEs
can be configured with multiple sets of measurement configurations,
one for individual handovers (for example, with lower thresholds)
and one for group handovers (for example, with higher thresholds).
A group handover is initiated only if the triggering conditions set
for a group handover are met. Note that the UEs may be unaware of
which measurement report configuration is for individual handover
and which is for group handover. UEs can simply treat them as
different configurations, and as such the techniques explained
herein can be implemented in a backward-compatible fashion. The
eNB, however, has to track which reporting configurations (and
related measurement IDs) are for individual UEs and which are for
the whole group.
[0117] Another option is to use individual configurations for a
group handover. When a certain number of measurement reports
indicating an impending handover are received within certain
duration, a group handover may be initiated. Note that in this
case, the first few UEs may be handed individually. After a group
handover has been initiated, the rest of the UEs within the group
will be handed over as a group.
[0118] Though most handovers are initiated in response to changes
in radio signals, it is possible, especially with heterogeneous
deployments, to initiate handovers for load balancing/offloading
reasons. In such cases, handovers can be initiated without
receiving measurement reports. The concept of group mobility can be
used here, where when the serving cells becomes overloaded or when
a neighboring cell becomes under-loaded and is able/willing to
offload some of the users of the serving cell, handover preparation
is started towards the concerned neighbor for all the UEs belonging
to the same group, or a subset of the UEs within the group.
Issuing a Group Handover Command by the eNB Via RRC to all UEs in
the Group at the Same Time.
[0119] If all the bearers of all the UEs that are being handed over
together as a group have been admitted at the target, and common
measurement and lower layer configurations are to be used for all
the UEs in the target cell, then the handover commands to be sent
to each UE will have these common features: [0120] a. measConfig
will contain the same info [0121] b. mobilityControlInfo, will
contain the same info except for the C-RNTI and the optional RACH
dedicated preamble to use. [0122] c. radioResourceConfigDedicated
IE, will have no DRBs to release and the UEs are already aware of
their own RBs. Thus, it is possible to broadcast the handover
command to the group of UEs. This can be done by, for example,
using a system information broadcast where the group mobility ID,
the target PCI, and the initial C-RNTI, as well as initial
dedicated preamble for the group are broadcasted. UEs belonging to
the broadcasted group ID will be informed that they are to execute
a handover to the broadcasted target PCI.
[0123] With regard to the C-RNTI, the above described technique
assumes that there is some group membership ID for each UE (for
example, assigned each time a UE is added to a group and
communicated to the UE). When the handover to a target is
requested, this membership ID could be indicated, or the source can
order the bearer lists according to an increasing/decreasing
membership ID of the UEs so that the target can become aware of the
ID indirectly. As an example, assume, the group has three members
with IDs 0, 1 and 2. When the target performs admission control, it
will allocate CRNT-Is 15, 16 and 17 to these UEs, and communicate
such information to the source in the handover request ACK. The
target, when it broadcasts the handover command, needs to include
C-RNTI value of 15. Each UE can find out the C-RNTI allocated to it
by adding the broadcasted C-RNTI and its membership ID. Similar
mechanisms can be used in the RACH dedicated preamble.
[0124] Another possibility is to broadcast the group handover
command from the target as well as the source, because in a
handover, UEs most probably experience better radio conditions with
the target than the source.
Preparing Handover Only to a Subset of Reported Neighbors.
[0125] A different strategy with respect to the first embodiment
described above may be used. In one embodiment the eNB waits for
several UEs in the same group to report strong neighbors before
initiating the preparation for handover. The eNB then performs
handover preparation for all UEs in the group toward a subset of
the reported neighbors selected based on different criteria such as
the ones listed below. The eNB can choose as candidate targets for
handover of the group of UEs:
1. The cell(s) reported by most UEs in the group; 2. The strongest
cell(s) reported by all the UEs in the group; 3. A combination of
the above two.
[0126] An exemplary flowchart of the embodiment is shown in FIG. 9.
It shall be pointed out that currently standardized mobility
procedures do not allow for parallel handover preparation for the
same UE(s) and towards different cells at the same eNB. However, to
overcome this problem, multiple handover preparations can be
achieved by including the secondary candidate target cells under
the same eNB (i.e. cells that are not the main handover preparation
target) in the cells listed in the RRC Container IE (present in
both the Source RNC to Target RNC Transparent Container IE--for
WCDMA inbound mobility--and Source eNB to Target eNB Transparent
Container IE--for LTE inbound mobility) or in the RRC Context IE in
the X2: HANDOVER REQUEST message. The eNB hosting the target cells
will prepare both the cell indicated as main target in the Target
Cell ID IE (contained in the source to target transparent
container) and the cells indicated as other reported cells in the
RRC Container.
[0127] In this embodiment, there is a trade-off between accurate
selection of target candidates and time available for handover
preparation. As the source eNB waits for more measurements from all
the UEs in the group in order to make a more accurate selection, it
will also have less time to perform the preparation and the actual
handover. On the other hand, if the eNB makes its decision based on
fewer UE measurements (or if it bases its decision only on a single
UE measurement report), the target(s) it selects might not be the
most appropriate for the whole group. Different thresholds or
criteria on how many measurements to consider and on how many
candidate targets to include in the preparation may be applied
depending on the particular situation. For example, how many times
a target has to be included in UE measurement reports before that
target is selected as a candidate can vary greatly according to the
deployment scenario and/or UE speed vs. cell density in the
coverage area.
[0128] It should be noted that the source can decide, instead of or
in addition to multiple handover preparations, to direct a subset
of the UEs to different targets. For example, if a group consists
of 10 UEs, the source may decide to prepare the first 3 UEs for a
handover towards cells A and B and the other 7 UEs towards cells A
and C. The methods described above to send the preparations,
handover request acknowledgements and handover commands are then
applicable to the subset of the UEs that are being handed over to
the same targets.
[0129] The source eNB can also gather statistics from UE groups
identified in the past, in order to learn how to prepare later
group handovers (e.g. in case multiple UE groups have been
identified having the same distinctive characteristics--two or more
groups of UEs on board a very long train, or on different trains
traveling along the same route). Statistics about handover
preparations can also be gathered per group instead of per cell
relation, and be reported to an OAM node.
Issuing a Single Path Switch Request.
[0130] In this embodiment, once the target eNB has completed an X2
based handover for the whole group of UEs, it can issue a single
PATH SWITCH REQUEST message to the MME containing some or all of
the following information: [0131] 1) the Mobility Group ID [0132]
2) The radio access bearer information in the E-RAB To Be Switched
in Downlink List IE for some or all of the UEs [0133] 3) UE Context
information for some or all of the UEs in the group such as
multiple eNB UE S1AP ID IE for all UEs in the Mobility Group;
multiple Source MME UE S1AP ID IE for all UEs in the Mobility
Group; multiple UE Security Capabilities IE for all UEs in the
Mobility Group.
[0134] The MME will be informed either implicitly or explicitly of
the Mobility Group ID and the list of its members either by the eNB
that first creates the group or by the eNB that first sends the
enhanced PATH SWITCH REQUEST message. [0135] If the eNB that first
creates the Mobility Group is to inform the MME of such event, such
process can either be achieved by means of new signaling over the
S1 or RANAP protocols or by means of existing procedures. As an
example, in an LTE system, procedures that can be reused are the
eNB DIRECT INFORMATION TRANSFER message or the UE CAPABILITY INFO
INDICATION message from the eNB to the MME. Either the new messages
or the existing ones will have to contain the Mobility Group IE and
UE identification IEs such as (in the LTE case) one or both the
S1AP IDs corresponding to each UE in the mobility group, namely one
or both of the eNB UE S1AP ID IE and MME UE S1AP ID IE. The
existing or new messages used in this mechanism may also be used to
amend the list of UEs in the mobility group. [0136] The MME
receiving this information stores it for future use. When messages
referring only to a Mobility Group ID are received by the MME, it
is possible to deduce that the Mobility Group ID refers to all the
UEs previously associated with such mobility group. [0137] If the
MME is implicitly informed of the mobility group creation, the MME
comes to know about the existence of the mobility group (i.e.
Mobility Group ID and member UEs) at first reception of the
enhanced PATH SWITCH REQUEST message described above. The MME may
be informed about changes to the mobility group purely by means of
following PATH SWITCH REQUEST messages. [0138] As described above,
the MME receiving this information stores it for future use. When
messages referring only to a Mobility Group ID are received by the
MME, it is possible to deduce that the Mobility Group ID refers to
all the UEs previously associated with such mobility group. For
example, after the first PATH SWITCH REQUEST message containing
Mobility Group ID IE and the details on member UEs is received,
provided that there are no changes to the mobility group, following
PATH SWITCH REQUEST messages in reference to handovers of the UEs
in the mobility group may contain only the Mobility Group ID. This
provides the MME the information about which bearers for each UE in
the mobility group need to be switched and how they should be
configured.
[0139] In S1 handovers, instead of PATH SWITCH messaging, the
target sends a HANDOVER NOTIFY message that tells the MME that the
UE has been identified in the target cell (i.e. have performed RACH
access and synchronized) and the MME can then issue the MODIFY
BEARER REQUEST command towards the SGW. Similar to the PATH SWITCH,
a single HANDOVER NOTIFY message can be used for communicating this
to the MME which can be done in several ways. For example: [0140]
Using lists instead of single entries in the MME UE S1AP ID and eNB
UE S1AP IDs (i.e. list of the IDs of all the UEs involved in the
group handover) [0141] Including the group ID in the HANDOVER
REQUEST from the MME to the target, which is then used in the
HANDOVER REQUEST ACK and HANDOVER NOTIFY to be sent towards the
MME
[0142] A MODIFY BEARER REQUEST is sent from the MME to the SGW in
response to a PATH SWITCH REQUEST for X2 handovers and a HANDOVER
NOTIFY for S1 handover. Either an individual request is sent for
each UE, or in the case of PATH SWITCH and HANDOVER NOTIFY, only
one message that includes the information of all the UEs that are
being handed over as a group is sent. Some of the IEs that require
change/update in this list are: (see 29.724 for all the fields
included I in MODIFY BEARER REQUEST): [0143] Mobile Equipment
Identity (MEI), which now becomes a list of all the UEs in the
group [0144] Bearer contexts to be modified, which now includes all
the admitted bearers of all the UEs [0145] Bearer contexts to be
removed, which now includes all the non-admitted bearers of all the
UEs
[0146] The MODIFY BEARER RESPONSE and PATH SWITCH REQUEST
ACKNOWLEDGE messages are updated in a similar fashion to the MODIFY
BEARER REQUEST and PATH SWITCH REQUEST, respectively, to include
information about all the UEs involved in the group handover.
[0147] There are at least two advantages with the first embodiment
described above. First, the handover has more time to complete,
especially for the late UEs that report neighbors after the early
UEs, thus avoiding or minimizing the risk of handover failures
especially when the group of UEs is moving at high speeds.
Secondly, it will give more time to the candidate target neighbors
to allocate appropriate resources for the UEs. It can also be
argued that by receiving several HANDOVER PREPARATION REQUEST
messages at the same time, it will be easier for the target eNBs to
accurately reserve appropriate resources for inpending handovers.
An additional advantage is the saved signaling because some UEs are
no longer needed to send measurement reports. This will also reduce
battery consumption by these UEs.
[0148] The advantage of the second embodiment described above is
that the handover command does not necessarily have to be sent to
each individual UE in the group, which can greatly reduce the
overall handover signaling overhead. Also, one of the major causes
of radio link failures is bad radio conditions experienced by a UE
when a handover command is sent to the UE causing the loss of the
handover command. Sending a handover command to all users in a
broadcast fashion and/or by both the source and the target cell can
ensure a timely and reliable reception of the command.
[0149] The advantage of the third embodiment described above is
that it offers the flexibility of optimizing accuracy in target
selection over gained time by making decision based on the first
few UE measurements, or optimizing gained time over accuracy in
target selection (deciding on fewer UE measurements, or even a
single one). The third embodiment can therefore be applied to
several use cases. For example, if UEs travel at a high speed it is
advantageous to optimize gained time for handover preparation. On
the other hand, if the UEs travel at lower speeds but possibly in
an urban scenario characterized by dense cell deployment, it will
be advantageous to optimize accuracy in handover target
selection.
[0150] The advantage of the fourth embodiment is that single PATH
SWITCH REQUEST/PATH SWITCH REQUEST ACK/HANDOVER NOTIFY/MODIFY
BEARER REQUEST/MODIFY BEARER RESPONSE messages are used for the
whole group rather than one message for each UE, thereby saving a
considerable amount of signaling to and from the core network. Such
advantage is more significant for large groups of UEs, as it may be
in the case of a high speed train carrying many UEs.
[0151] Embodiments described herein also relate to a base station
operable in a wireless communication system. The base station is
adapted to perform at least one embodiment of the method described
above. The base station is associated with the same technical
features, objects and advantages as the method described above and
illustrated e.g. in FIG. 1. The base station will be described in
brief in order to avoid unnecessary repetition.
[0152] Below, an exemplifying base station 1000, adapted to enable
the performance of an above described method for mobility
procedures will be described with reference to FIG. 10. The part of
the base station which is most is most affected by the adaptation
to the herein described method is illustrated as an arrangement
1001, surrounded by a dashed line. The base station could be e.g.
an eNB, or a NodeB, depending on in which type of communication
system it is operable, e.g. LTE or WCDMA. The base station 1000 and
arrangement 1001 is further illustrated as to communicate with
other entities via a communication unit 1002 which may be regarded
as part of the arrangement 1001. The arrangement or network node
may further comprise other functional units 1009, such as e.g.
functional units providing regular eNB functions, and may further
comprise one or more storage units 1008.
[0153] The arrangement 1001 could be implemented e.g. by one or
more of: a processor or a micro processor and adequate software and
memory for storing thereof, a Programmable Logic Device (PLD) or
other electronic component(s) or processing circuitry configured to
perform the actions described above, and illustrated e.g. in FIG. 1
or 5.
[0154] The arrangement part of the base station may be implemented
and/or described as follows:
The base station comprises a receiving unit 1005, adapted to
receive, from a first UE in the UE group, a mobility related
parameter associated with the first UE The base station further
comprises a determining unit 1006, adapted to determine whether to
initiate a mobility related procedure for a second UE in the UE
group based on the received mobility related parameter; and further
comprises a mobility control unit 1007, adapted to initiate the
mobility related procedure for the second UE when it is determined
that the mobility related procedure is to be performed.
[0155] The determining may comprise determining whether to initiate
a mobility related procedure for the first UE based on the received
mobility related parameter and applying the result on the second UE
belonging to the same group.
[0156] The mobility related procedure may be a handover
procedure.
[0157] The base station may be adapted to initiate the mobility
related procedure by transmitting a handover request to a target
network node.
[0158] The mobility related parameter may be one or more of: [0159]
a report of a measured signal strength at the first UE; [0160] a
report of a measurement on a signal received by the first UE from a
neighboring base station; [0161] information on the geographical
position of the first UE; and [0162] a report of a measurement on a
signal received by the first UE from an access point in another
wireless communication system.
[0163] The base station may be adapted to receive a respective
mobility related parameter associated with a number of other UEs in
the UE group; and the initiating of the mobility related procedure
may further be based on said received number of mobility related
parameters.
[0164] The base station may be adapted to initiate the mobility
related procedure towards a cell, which cell is reported as being a
neighbor cell by the largest number of UEs in the UE group or which
cell is the strongest cell reported by a plurality of UEs in the UE
group
[0165] The mobility related procedure may be initiated for a
plurality of UEs in the UE group, said plurality comprising the
second UE, or even for the whole UE group.
[0166] The initiating may comprise using a single mobility command
for a plurality of UEs in the UE group.
[0167] Embodiments described herein also relate to a network node
operable in a communication system. The network node is adapted to
perform at least one embodiment of the method described above e.g.
in association with FIG. 2. The network node is operable to be
associated with a handover of a plurality of UEs in a UE group,
said UE group comprising UEs having correlated mobility related
parameters. The network node is associated with the same technical
features, objects and advantages as the method to be performed by a
network node, which method is described above. The network node
will be described in brief in order to avoid unnecessary
repetition.
[0168] Below, an exemplifying network node 1100, adapted to enable
the performance of an above described method for mobility
procedures will be described with reference to FIG. 11. The part of
the network node which is most affected by the adaptation to the
herein described method is illustrated as an arrangement 1101,
surrounded by a dashed line. The network node could be a base
station such as an eNB, or an MME node in a communication system.
The network node 1100 and arrangement 1101 is further illustrated
as to communicate with other entities via a communication unit 1102
which may be regarded as part of the arrangement 1101. The
arrangement or network node may further comprise other functional
units 1109, such as e.g. functional units providing regular eNB or
MME functions, and may further comprise one or more storage units
1108.
[0169] The arrangement 1101 could be implemented e.g. by one or
more of: a processor or a micro processor and adequate software and
memory for storing thereof, a Programmable Logic Device (PLD) or
other electronic component(s) or processing circuitry configured to
perform the actions described above, e.g. in conjunction with FIG.
2.
[0170] The arrangement part of the network node may be implemented
and/or described as follows:
The network node comprises a receiving unit 1105, adapted to
receive information indicating that the plurality of UEs being
subjected to the handover have connected to a target node. The
network node further comprises a control unit 1107, adapted to
transmit a single path switch request or a single modify bearer
request for the plurality of the UEs in the UE group being
subjected to the handover. The network node is illustrated as
comprising a determining unit 1106, which may be adapted e.g. to
analyze the received information and to trigger the control unit
when determined adequate. Such functions could alternatively or in
addition be performed in the receiving unit 1105 and/or the control
unit 1107, which would then be adapted to perform such actions
[0171] The network node may be the target node, to which the
plurality of UEs mentioned above is handed over.
[0172] Embodiments described herein also relate to a UE operable in
a wireless communication system. The UE is adapted to perform at
least one embodiment of the method described above. The base
station is associated with the same technical features, objects and
advantages as the method described above and illustrated e.g. in
FIG. 3. The UE will be described in brief in order to avoid
unnecessary repetition.
[0173] Below, an exemplifying UE 1200, adapted to enable the
performance of an above described method for mobility procedures
will be described with reference to FIG. 12. The part of the UE
which is most affected by the adaptation to the herein described
method is illustrated as an arrangement 1201, surrounded by a
dashed line. The UE could be operable, e.g. in an LTE and/or WCDMA
system or in a multi-RAT system. The UE 1200 and arrangement 1201
are further illustrated as to communicate with other entities via a
communication unit 1202 which may be regarded as part of the
arrangement 1201. The arrangement or network node may further
comprise other functional units 1209, such as e.g. functional units
providing regular UE functions, and may further comprise one or
more storage units 1208.
[0174] The arrangement 1201 could be implemented e.g. by one or
more of: a processor or a micro processor and adequate software and
memory for storing thereof, a Programmable Logic Device (PLD) or
other electronic component(s) or processing circuitry configured to
perform the actions described above, and illustrated e.g. in FIG.
3.
[0175] The UE is operable to be comprised in, i.e. to belong to, a
UE group comprising UEs having correlated mobility related
parameters, and operable to have access to, e.g. receive and store,
a first identifier identifying the UE group in which the first UE
is comprised.
[0176] The arrangement part of the UE may be implemented and/or
described as follows:
The UE comprises a receiving unit 1205, adapted to receive a
broadcasted mobility related command from a base station, said
command comprising a second identifier, identifying a UE group. The
UE further comprises a determining unit 1206, adapted to determine,
based on the first and second identifier, whether the UE belongs to
the UE group identified by the second identifier. The UE further
comprises a mobility response unit 1207, adapted to respond to the
received command when it is determined that the UE belongs to the
UE group identified by the second identifier.
[0177] The UE may further be operable to be associated with an
identity within the UE group, and the received mobility related
command may further comprise a CRNT-I assigned to a UE in the UE
group, which UE group is identified by the second identifier. The
UE may then be further adapted to determine, when the first UE
belongs to the UE group identified by the second identifier, a
CRNT-I, assigned to the first UE, based on the identity, e.g. a
number, within the UE group and the CRNT-I comprised in the
mobility related command.
[0178] FIG. 13 schematically shows an embodiment of an arrangement
1300 which may be used in a network node 1000. Comprised in the
arrangement 1300 are here a processing unit 1306, e.g. with a DSP
(Digital Signal Processor). The processing unit 1306 may be a
single unit or a plurality of units to perform different actions of
procedures described herein. The arrangement 1300 may also comprise
an input unit 1302 for receiving signals from other entities, and
an output unit 1304 for providing signal(s) to other entities. The
input unit and the output unit may be arranged as an integrated
entity or as illustrated in the example of FIG. 13.
[0179] Furthermore, the arrangement 1300 comprises at least one
computer program product 1308 in the form of a non-volatile or
volatile memory, e.g. an EEPROM (Electrically Erasable Programmable
Read-Only Memory), a flash memory and a hard drive. The computer
program product 1308 comprises a computer program 1310, which
comprises code means, which when executed in the processing unit
1306 in the arrangement 1300 causes the arrangement 1300 and/or the
base station in which it is comprised to perform the actions e.g.
of the procedure described earlier in conjunction with FIG. 1.
[0180] The computer program 1310 may be configured as a computer
program code structured in computer program modules 1310a-1310d.
Hence, in an exemplifying embodiment, the code means in the
computer program of the arrangement 1300 comprises a receiving
module 1310a, for receiving a mobility related parameter associated
with a first UE. The computer program may further comprise a
determining module 1310b, for determining whether to initiate a
mobility related procedure for a second UE in the UE group based on
the received mobility related parameter. The computer program
further comprises an initiating module 1310c, for initiating the
mobility related procedure for the second UE when it is determined
that the mobility related procedure is to be performed. The
computer program may further comprise further modules, illustrated
as module 1310d, e.g. for controlling and performing other mobility
related procedures associated with a UE group.
[0181] The computer program modules could essentially perform the
actions of the flow illustrated in FIG. 1, to emulate the
arrangement 1001 in the network node 1000. In other words, when the
different computer program modules are executed in the processing
unit 1306, they may correspond e.g. to the units 1005-1007 of FIG.
10.
[0182] It is to be understood that corresponding arrangements, as
the one for a base station described above, could be implemented
also for a network node and a UE. The structure could be the same,
but the computer program modules would then be arranged to comprise
code, which when executed in the processing unit would perform or
trigger the performing of the actions described e.g. in conjunction
with FIGS. 2 and 3 above.
[0183] Although the code means in the embodiments disclosed above
in conjunction with FIG. 13 are implemented as computer program
modules which when executed in the processing unit causes the test
device to perform the actions described above in the conjunction
with figures mentioned above, at least one of the code means may in
alternative embodiments be implemented at least partly as hardware
circuits.
[0184] The processor may be a single CPU (Central processing unit),
but could also comprise two or more processing units. For example,
the processor may include general purpose microprocessors;
instruction set processors and/or related chips sets and/or special
purpose microprocessors such as ASICs (Application Specific
Integrated Circuit). The processor may also comprise board memory
for caching purposes. The computer program may be carried by a
computer program product connected to the processor. The computer
program product may comprise a computer readable medium on which
the computer program is stored. For example, the computer program
product may be a flash memory, a RAM (Random-access memory) ROM
(Read-Only Memory) or an EEPROM, and the computer program modules
described above could in alternative embodiments be distributed on
different computer program products in the form of memories within
the test device.
[0185] It is to be understood that the choice of interacting units,
as well as the naming of the units within this disclosure are only
for exemplifying purpose, and nodes suitable to execute any of the
methods described above may be configured in a plurality of
alternative ways in order to be able to execute the suggested
procedure actions.
[0186] It should also be noted that the units described in this
disclosure are to be regarded as logical entities and not with
necessity as separate physical entities.
[0187] While the embodiments have been described in terms of
several embodiments, it is contemplated that alternatives,
modifications, permutations and equivalents thereof will become
apparent upon reading of the specifications and study of the
drawings. It is therefore intended that the following appended
claims include such alternatives, modifications, permutations and
equivalents as fall within the scope of the embodiments.
[0188] FIG. 14 illustrates an exemplary network node processing
unit that is configured to identify UE mobility groups and manage
the UEs belonging to a UE mobility group as a group. The node in
FIG. 14 includes an S1 interface that enables the node to
communicate with mobility management entities (MMEs), an X2
interface unit that enables the node to communicate with other
nodes, and a radio interface unit that enables the node to
communicate with UEs. The X2 interface unit is configured to
receive information about UEs from other base stations or nodes.
Such information may comprise UE History Information or other radio
access technologies monitored by the UE. The radio interface unit
is configured to communicate with the served UEs, including
configuring measurement reporting from such UEs. The radio
circuitry can be configured to reconfigure the measurement
reporting of UEs to validate and verify that UEs are appropriately
included in a given Mobility Group.
[0189] The node also includes a UE measurement unit that performs
various measurements to obtain, e.g., trend information associated
with each UE. The node also includes a Mobility Group management
Unit that identifies UE groups based on the measurements or trend
information obtained for the UEs and manages the UE groups for
mobility events or resource allocation. The Mobility Group
management unit is configured to use the information provided by
the UE or by other network nodes to evaluate whether one or more
UEs are moving according to the same trends and shall be grouped
together in a Mobility Group. The node also includes a memory for
storing UE measurement data and other necessary information
required by the various units of the node.
[0190] An exemplary UE configured to practice the above described
methods is illustrated in FIG. 15. The apparatus is arranged with
radio circuitry to communicate with network nodes, a memory to
store information related to the disclosed solution, and a
processing unit that is configured to receive and process commands
from network nodes. For example, the processing unit is configured
to process a group handover command issued by an eNB, or other
commands related to group handover as described above.
[0191] Those skilled in the art will appreciate that the functions
and means explained herein below may be implemented using software
functioning in conjunction with a programmed microprocessor or
general purpose computer, and/or using an application specific
integrated circuit (ASIC). It will also be appreciated that while
embodiments of the disclosed solution are primarily described in
the form of methods and nodes, they may also be embodied in a
computer program product as well as in a system comprising a
computer processor and a memory coupled to the processor, wherein
the memory is encoded with one or more programs that may perform
the functions disclosed herein.
APPENDIX TO DETAILED DESCRIPTION
[0192] In the foregoing part of the detailed description, it is
referred to different mobility related parameters in a wireless
communication system, such as an LTE system. For the interested, a
description of some of these mobility related parameters and their
use follows below. It is placed at the end of the detailed
description in order not to obscure the understanding of the herein
suggested solution.
LTE Architecture.
[0193] The third generation partnership project (3GPP) is currently
working on standardization of Release 12 of the Long Term Evolution
(LTE) concept. The architecture of the LTE system as shown in FIG.
16 includes radio access nodes (eNBs) and evolved packet core nodes
(MME/S-GW).
[0194] An exemplary management system that will be referenced in
the later sections of this disclosure is shown in FIG. 17. The node
elements (NE), also referred to as eNodeB or eNB, are managed by a
domain manager (DM), also referred to as the operation and support
system (OSS). A DM may further be managed by a network manager
(NM). The interface between the two NEs is X2 interface, whereas
the interface between the two DMs is referred to as Itf-P2P. The
management system may perform configuration as well as monitoring
of the network elements, e.g., receive observations/measurements
associated with features of the network elements. For example, the
DMs in FIG. 17 monitor and configure the NEs, while the NM monitors
and configures the DMs, as well as the NEs via the DMs.
[0195] In this disclosure, it is further assumed that any function
that automatically optimizes NE parameters can in principle be
executed by a NE, DM, or a NMS. Such features are referred to as
Self-Organizing Network (SON) features.
Cell Selection
[0196] The idle mode cell selection and reselection procedure in
LTE [3GPP 36.304] is based on both stored information and
information acquired from broadcasted system information, and
evaluations of radio frequency measurements by the UE.
[0197] The cell selection evaluation process is based on a
criterion S, which is fulfilled when:
Srxlev>0 AND Squal>0
where:
Srxlev=Qrxlevmeas-(Qrxlevmin+Qrxlevminoffset)-Pcompensation;
Squal=Qqualmeas-(Qqualmin+Qqualminoffset).
where:
TABLE-US-00001 Srxlev Cell selection RX level value (dB) Squal Cell
selection quality value (dB) Q.sub.rxlevmeas Measured cell RX level
value (RSRP) Q.sub.qualmeas Measured cell quality value (RSRQ)
Q.sub.rxlevmin Minimum required RX level in the cell (dBm)
Q.sub.qualmin Minimum required quality level in the cell (dB)
Q.sub.rxlevminoffset Offset to the signalled Q.sub.rxlevmin taken
into account in the Srxlev evaluation as a result of a periodic
search for a higher priority PLMN while camped normally in a VPLMN
Q.sub.qualminoffset Offset to the signalled Q.sub.qualmin taken
into account in the Squal evaluation as a result of a periodic
search for a higher priority PLMN while camped normally in a VPLMN
Pcompensation max(P.sub.EMAX-P.sub.PowerClass, 0) (dB) P.sub.EMAX
Maximum TX power level an UE may use when transmitting on the
uplink in the cell (dBm) defined as P.sub.EMAX in [TS 36.101]
P.sub.PowerClass Maximum RF output power of the UE (dBm) according
to the UE power class as defined in [TS 36.101]
[0198] The signaled values Qrxlevminoffset and Qqualminoffset are
only applied when a cell is evaluated for cell selection as a
result of a periodic search by a UE for a higher priority PLMN
(Public Land Mobile Network) while camped normally in a VPLMN
(Visited Public Land Mobile Network). During a periodic search for
higher priority PLMN, the UE may check the S criteria of a cell
using parameter values stored from a different cell of this higher
priority PLMN.
UE Measurements.
[0199] UEs can be configured to report measurements, for example,
to support mobility. As specified in 3GPP TS 36.331, the E-UTRAN
standards provide a measurement configuration applicable for a UE
in RRC_CONNECTED by means of dedicated signaling, i.e. using the
RRCConnectionReconfiguration message. The following measurement
configurations can be signaled to the UE: [0200] Measurement
objects: These define on what the UE should perform the
measurements--such as a carrier frequency. The measurement objects
may also include a list of cells to be considered (white-list or
black-list) as well as associated parameters, e.g. frequency- or
cell-specific offsets. [0201] Reporting configurations: These
consist of the periodic or event-triggered criteria which cause the
UE to send a measurement report, as well as the details of what
information the UE is expected to report (e.g. the quantities, such
as Received Signal Code Power (RSCP) for UMTS or Reference Signal
Received Power (RSRP) for LTE, and the number of cells). [0202]
Measurement identities: These identify a measurement and define the
applicable measurement object and reporting configuration. Each
measurement identity links one measurement object with one
reporting configuration. By configuring multiple measurement
identities it is possible to link more than one measurement object
to the same reporting configuration, as well as to link more than
one reporting configuration to the same measurement object. The
measurement identity is used as a reference number in the
measurement report. [0203] Quantity configurations: The quantity
configuration defines the filtering to be used on each measurement.
One quantity configuration is configured per RAT type, and one
filter can be configured per measurement quantity. [0204]
Measurement gaps: Measurement gaps define time periods when no
uplink or downlink transmissions will be scheduled, so that the UE
may perform the measurements (e.g. inter-frequency measurements
where the UE has only one Tx/Rx unit and supports only one
frequency at a time). The measurement gaps are common for all
gap-assisted measurements
[0205] In E-UTRAN standards, only a single measurement object is
configured for a given frequency, but more than one measurement
identity may use the same measurement object. The identifiers used
for the measurement object and reporting configuration are unique
across all measurement types. It is possible to configure the
quantity that triggers the report (RSCP or RSRP) for each reporting
configuration.
[0206] In LTE, the most important measurement metric used are the
Reference Signal Received Power (RSRP) and Reference Signal
Received Quality (RSRQ). RSRP is a cell specific measure of signal
strength and it is mainly used for ranking different cells for
handover and cell reselection purposes. It is calculated as the
linear average of the power of the Resource Elements (REs) which
carry cell-specific Reference Signals (RSs). The RSRQ, on the other
hand, also takes the interference into consideration by taking the
total received wideband power into account as well.
[0207] One of the measurement configuration parameters that UEs
receive from their serving eNBs is the S-measure, which tells the
UE when to start measuring neighboring cells. If the measured RSRP
of the serving cell falls below the S-measure, indicating the
signal of the serving cell is no longer as strong as previously
measured, the UE starts measuring the signal strength of RSs from
the neighboring cells. The S-measure is an optional parameter and
different S-measure values can be specified for initiating
intra-frequency, inter-frequency and inter-RAT measurements.
[0208] Once the UE is enabled for measuring, it can report any of
the following: [0209] The serving cell [0210] Listed cells (i.e.
cells indicated as part of the measurement object); [0211] Detected
cells on a listed frequency (i.e. cells which are not listed cells
but are detected by the UE). There are several measurement
configuration parameters that specify the triggering of measurement
reports from the UE. The following event-triggered criteria are
specified for intra-RAT measurement reporting in LTE: [0212] Event
A1: Primary serving cell (PCell) becomes better than an absolute
threshold. [0213] Event A2: PCell becomes worse than an absolute
threshold. [0214] Event A3: Neighbour cell becomes better than an
offset relative to the PCell. [0215] Event A4: Neighbour cell
becomes better than an absolute threshold. [0216] Event A5: PCell
becomes worse than one absolute threshold and neighbour cell
becomes better than another absolute threshold. [0217] Event A6:
Neighbour cell becomes better than an offset relative to a
secondary cell (SCell) For inter-RAT mobility, the following
event-triggered reporting criteria are specified: [0218] Event B1:
Neighbour cell becomes better than an absolute threshold. [0219]
Event B2: Serving cell becomes worse than one absolute threshold
and neighbour cell becomes better than another absolute threshold.
The most widely used measurement report triggering event related to
handover is A3, and its usage is illustrated in FIG. 18. The
triggering conditions for event A3 can be formulated as:
[0219] N>S+HOM (1)
where N and S are the signal strengths of the neighboring and
serving cells, respectively, and HOM is the handover margin. HOM is
the difference between the radio quality of the serving cell and
the radio quality needed before attempting a handover. The radio
quality is measured either using RSRP or RSRQ (see 3GPP TS 36.133
for further explanation).
[0220] The UE triggers the intra-frequency handover procedure by
sending event A3 report to the serving eNB. This event occurs when
the UE discovers that the target cell is better than the serving
cell with a margin "HOM". The UE is configured over RRC when
entering a cell and the HOM is calculated from the following
configurable parameters:
HOM=Ofs+Ocs+Off-Ofn-Ocn+Hys;
where:
[0221] Ofs is the frequency specific offset of the serving
cell,
[0222] Ocs is the cell specific offset (CIO) of the serving
cell,
[0223] Off is the a3-Offset,
[0224] Ofn is the frequency specific offset of the neighbor
cell,
[0225] Ocn is the CIO of the neighbor cell,
[0226] Hys is the hysteresis.
If the condition in (1) is satisfied and it remains valid for a
certain duration known as Time To Trigger (TTT), the UE sends a
measurement report to the serving eNB (in FIG. 18, event A3 is
satisfied at point A and measurement report is sent at point B in
time). When the serving eNB receives the measurement report, it can
initiate a handover towards the neighboring cell.
[0227] In addition to event-triggered reporting, the UE may be
configured to perform periodic measurement reporting. In such case,
the same parameters configured for event-triggered reporting may be
used, except that the UE starts reporting immediately rather than
only after the occurrence of an event.
LTE Mobility in Connected Mode
[0228] The LTE handover preparation and execution can essentially
be completed over the X2 interface without involving the core
network. However, some details needs to be passed or negotiated
between network nodes over S1. The handover mechanism can also be
handled via the S1 interfaces forwarded by the MME. The following
discussion is based on a basic handover scenario in which neither
MME nor S-GW changes due to the handover. See 3GPP TS 36.300 for
more details.
[0229] In referring to FIG. 4, control plane steps involved in a
basic handover scenario include: [0230] 1 The source eNB configures
the UE measurement procedures. [0231] 2 The UE is triggered to send
MEASUREMENT REPORT by the rules set by, e.g., system information,
specification, etc. [0232] 3 The source eNB makes the decision
based on MEASUREMENT REPORT and RRM information to hand off the UE.
[0233] 4 The source eNB issues a HANDOVER REQUEST message to the
target eNB passing necessary information to prepare the handover at
the target side [0234] 5 Admission Control may be performed by the
target eNB. [0235] 6 The target eNB prepares HO with L1/L2 and
sends the HANDOVER REQUEST ACKNOWLEDGE to the source eNB. The
HANDOVER REQUEST ACKNOWLEDGE message includes a transparent
container with mobilityControlInformation to be sent to the UE as
an RRC message to perform the handover. The HANDOVER REQUEST
ACKNOWLEDGE message includes an Information Element (IE) called
"Target eNB to Source eNB Transparent Container". This IE basically
contains the handover command message (RRCConnectionReconfiguration
that includes the mobilityControlInfo IE) that is sent to the UE in
the next step. [0236] NOTE: As soon as the source eNB receives the
HANDOVER REQUEST ACKNOWLEDGE, or as soon as the transmission of the
handover command is initiated in the downlink, user plane data
forwarding may be initiated. [0237] 7 The source eNB sends the RRC
message to the UE to perform the handover, e.g., an
RRCConnectionReconfiguration message including the
mobilityControlInfo, which was received in the transparent
container included in the HANDOVER REQUEST ACKNOWLEDGE sent from
the target. [0238] 8 The source eNB sends the SN STATUS TRANSFER
message to the target eNB. [0239] 9 After receiving the
RRCConnectionReconfiguration message including the
mobilityControlInformation, the UE performs synchronization with
target eNB and accesses the target cell via RACH (Random Access
Channel). [0240] 10 The target eNB responds with a UL allocation
and a timing advance. [0241] 11 When the UE has successfully
accessed the target cell, the UE sends the
RRCConnectionReconfigurationComplete message (C-RNTI) to the target
eNB to confirm the handover. The target eNB begins sending data to
the UE. [0242] 12 The target eNB sends a PATH SWITCH REQUEST
message to the MME to inform that the UE has changed cell. [0243]
13 The MME sends a MODIFY BEARER REQUEST message to the Serving
Gateway. [0244] 14 The Serving Gateway switches the downlink data
path to the target side. The Serving gateway sends one or more "end
marker" packets on the old path to the source eNB and releases any
U-plane/TNL resources towards the source eNB. [0245] 15 The Serving
Gateway sends a MODIFY BEARER RESPONSE message to the MME. [0246]
16 The MME confirms the PATH SWITCH REQUEST message with the PATH
SWITCH REQUEST ACKNOWLEDGE message. [0247] 17 By sending the UE
CONTEXT RELEASE message, the target eNB informs the source eNB of
the success of the handover and triggers the release of resources
by the source eNB. [0248] 18 Upon receiving the UE CONTEXT RELEASE
message, the source eNB releases radio and C-plane related
resources associated with the UE context. Any ongoing data
forwarding may continue.
Intra-Frequency Neighbor Cell Measurements.
[0249] Handover candidates, such as eNBs or cells, are regularly
monitored by UEs. A UE synchronizes with a neighbor cell candidate
using synchronization signals and identifies a candidate cell using
physical signal sequences that are associated with a physical cell
identifier. Furthermore, the physical cell identifier of a cell is
associated with a cell-specific reference sequence (pilot), from
which a UE can estimate the reference symbol received power (RSRP).
RSRP essentially is the average power of the reference sequence
(pilot) symbols. In addition, a UE can determine the reference
symbol received quality by dividing the RSRP by the total received
power.
Random Access in LTE
[0250] Random access (RA) procedures serve as an uplink control
procedure that grants UE access to the network.
[0251] A RA procedure serves two main purposes: [0252] It lets a UE
align its UL timing to the timing as expected by the eNB in order
to minimize interference between transmissions of different UEs. UL
time alignment is a requirement in E-UTRAN standards that needs to
be satisfied before data transmissions by a UE can commence. [0253]
It provides a means for a UE to notify the network of its presence
and for the eNB to grant the UE initial access to the system.
[0254] In addition to being used during initial access, RA
procedures can also be used when a UE loses uplink synchronization
or when a UE is in an idle or a low-power mode.
[0255] A basic RA procedure is a four-phase procedure as outlined
in FIG. 19. The four phases are: [0256] Phase 1 comprises
transmission of a random access preamble by the UE, allowing the
Node B to estimate the transmission timing of the UE. Uplink
synchronization is necessary as the UE otherwise cannot transmit
any uplink data. [0257] Phase 2 comprises transmission by the
network of a timing advance command to correct the uplink timing,
based on the timing of arrival measurement in the first step. In
addition to establishing uplink synchronization, the second step
also assigns uplink resources and temporary identifier to the UE to
be used in the third step in the random access procedure. [0258]
Phase 3 comprises signalling from the UE to the eNB. A primary
function of this message is to uniquely identify the UE. The exact
content of this signalling depends on the state of the UE, e.g.,
whether it is previously known to the network or not. [0259] Phase
4, the final phase, is responsible for contention resolution in
case multiple UEs tries to access the system on the same resource.
In case of handover, it is possible to reserve a preamble in the
mobilityControl Information, which means that the UE is uniquely
identified already after Phase 2.
Position Determination in LTE
[0260] In a LTE system, several different localization methods are
available for determining the position of a UE.
[0261] The first localization method uses the network-assisted
version of Global Navigation Satellite Systems (GNSSs) like the
Global Positioning System (GPS) or Galileo. Different GNSSs can be
used individually or in combination with other GNSSs. The network
assists the UE GNSS receiver by providing assistance data (e.g.,
visible satellite list, clock corrections, reference positions) to
reduce the UE GNSS start-up and acquisition times, to increase the
UE GNSS sensitivity, and to allow the UE to consume less handset
power than with stand-alone GNSS. The network-assisted GNSS methods
rely on signaling between UE GNSS receivers and a continuously
operating GNSS reference receiver network which has clear sky
visibility of the same GNSS constellation as the assisted UE. With
GNSS the highest accuracy can be achieved which meets the FCC
requirements.
[0262] The second localization method is the Observed Time
Difference Of Arrival (OTDOA) method. This method utilizes the
differences of time measurements of downlink radio signals from at
least three eNBs along with the knowledge of the geographical
coordinates of the measured eNBs and their relative downlink timing
for calculating the position of a UE. A Positioning Reference
Signal (PRS) with a frequency reuse of six in combination with
low-interference subframes (LIS) is also introduced in order to
increase the visibility of the eNBs.
[0263] The third localization method, the enhanced cell ID
positioning method, utilizes information about the serving cell and
the knowledge of the geographical coordinates of the serving eNB
for UE position estimation. Additional radio resource measurements
like the Reference Signal Received Power (RSRP) or the Reference
Signal Received Quality (RSRQ) can be used to improve UE location
estimate. Also timing advance and AoA (Angle of Arrival) that are
estimated proprietarily in a base station or an eNB can be
considered for E-CID.
[0264] The fourth localization method determines how far a UE is
located from a eNB. This method estimates the round-trip time
between a mobile and its serving base station. LTE system is used
as an example in the following discussion. Other radio access
technologies apply as well.
[0265] It is specified in 3GPP TS 36.211 that "transmission of the
uplink radio frame number from the UE shall start N.sub.TAT.sub.s
seconds before the start of the corresponding downlink radio frame
at the UE", where T.sub.s is the LTE basic time unit,
Ts=1/(2048*15000) seconds. This is illustrated in FIG. 20.
[0266] The first uplink timing correction is sent from the eNB to
the mobile during random access, to give the mobile the initial
uplink timing. From then and onwards, adequate uplink timing is
maintained by sending timing advance commands to the mobile. Timing
advance commands are based on estimated uplink timing of the mobile
as illustrated by FIG. 20.
[0267] Based on timing misalignment measurements .DELTA.t, the eNB
sends quantized corrections to the mobile in step 1 (see below).
The mobile updates its timing in step 2 (see below).
[0268] 1 Quantization:
Q ( .DELTA. t ( k ) ) = round ( .DELTA. t ( k ) 16 T s )
##EQU00001##
[0269] 2 Timing update in the mobile:
N.sub.TA(k+1)=N.sub.TA(k)+16Q(.DELTA.t(k))
There are two alternative ways of estimating the round-trip time
between a mobile and an eNB. One alternative is using the timing
advanced commands. The quantized timing misalignment measurements
are tallied also on the base station side to form an estimate of
RTT:
N.sub.TA(k+1)=N.sub.TA(k)+16Q(.DELTA.t(k))
R{circumflex over (T)}T(k+1)=N.sub.TA(k+1)T.sub.s
The accuracy of the RTT estimate using the above equation is mainly
limited by the quantization, which means that a representative RTT
distribution is uniform with a width of 16T.sub.s:
p(R{circumflex over (T)}T(k+1))=U(R{circumflex over
(T)}T(k+1)-8T.sub.s,R{circumflex over (T)}T(k+1)+8T.sub.s)
The second alternative is using timing misalignment measurements.
Quantization is needed to limit the signalling to the mobile.
However, a more accurate misalignment measurement can also be
considered to form an estimate of RTT:
N TA ( k + 1 ) = N TA ( k ) + 16 Q ( .DELTA. t ( k ) ) ##EQU00002##
N ^ TA ( k + 1 ) = N TA ( k ) + 1 T s ( .DELTA. t ( k ) )
##EQU00002.2## R T ^ T ( k + 1 ) = N ^ TA ( k + 1 ) T s
##EQU00002.3##
In the second alternative, the accuracy of the estimated RTT is
limited by the timing misalignment accuracy. One typical assumption
is that the estimation error is zero-mean Gaussian with
variance.sup..sigma..sup.misal.sup.2. Thus, the RTT estimate
distribution is given by:
p ( RTT ) = 1 .sigma. misal 2 .pi. - ( RTT - R T ^ T ( k + 1 ) ) 2
/ 2 / .sigma. misali ##EQU00003##
Moreover, the RTT can also be expressed as:
R{circumflex over (T)}T.sub.i=2|p.sub.m-p.sub.i|/c+w.sub.i.
[0270] In summary, different positioning methods are described in
the above section. A hybrid positioning method incorporating
multiple positioning methods introduced above can be also
supported. The position information of a UE may be reported
together with the estimated errors (uncertainty) of the position
estimate and the velocity of the UE. The uncertainty of the
position information depends on the used method used, the position
of the UE within the coverage area, and the activity of the UE.
Movement Determination in LTE
Direction of Departure Estimation
[0271] Direction of departure estimation based on downlink signals
determines the angle of a mobile's movement as viewed from the base
station's perspective with respect to a certain reference. One
typical reference is a compass that designates north as 0 degree
and increases clockwise to 360 degrees when it is once again north.
Another exemplary reference uses complex numbers, using 0 degree to
designate the positive real axis and increasing counter-clockwise
up to 180 degrees when reaching the negative positive axis and
decreasing clockwise to -180 degrees when reaching the negative
positive axis. Note that the angle of arrival as observed by the
mobile is the direction of departure observed at the base station
plus a 180 degree offset.
Basic Method:
[0272] One basic direction of departure estimation method uses the
beam direction of a serving cell. Assuming that the mobile is
always within an angular range half way to neighboring cells at the
same site, the estimation error distribution would be uniform
within that range.
Subspace Methods:
[0273] Direction of departure estimation is most commonly done at a
base station equipped with multiple antennas and often relies on
coherent combination of per-antenna received signals. Popular
approaches include subspace methods for frequency estimation, where
the signal space and the noise space are separated--each spanned by
eigen-vectors associated with corresponding singular values.
Another popular approach is MUSIC (MUltiple Signal Classification)
based on a direct singular value decomposition, ESPRIT (Estimation
Of Signal Parameters via Rotational Invariance Techniques).
The Basics of Received Signal Strength Methods
[0274] These methods can also be used with less detailed
information such as received signal strengths and antenna
information.
[0275] The received signal strength pR (RSRP in LTE) can be
expressed as
P.sub.R=P.sub.T+g.sub.L+g.sub.A+g.sub.P+.omega.
where [0276] p.sub.T--transmitted pilot power, [0277] g.sub.L--gain
(<0) due to losses due to feeder cables etc, [0278]
g.sub.A--antenna gain (typically >0), [0279]
g.sub.P--propagation gain (<0), [0280] w--measurement noise.
[0281] FIG. 21 illustrates the situation for a specific direction
to a mobile receiving signals from sectors at the same site.
[0282] A reasonable assumption is that the propagation gain from
two sectors at the same site is the same. Furthermore, the pilot
powers and losses in the tower are either equal considering two
different sectors at the same site, or the difference is known.
Without loss of generality, it is assumed that the pilot power and
the tower losses are the same. This means that the difference
between the received signal strengths from two different sectors at
the same site as
p.sub.R1-p.sub.R3=p.sub.T+g.sub.L+g.sub.A1+g.sub.P+.omega..sub.1-p.sub.T-
-g.sub.L-g.sub.A3-g.sub.P.omega..sub.2=g.sub.A1-g.sub.A3+.omega..sub.1-.om-
ega..sub.3
[0283] Hence, the received signal strength difference is equal to
the antenna gain difference plus noise. If the noise per measured
sector is considered independent and of variance
.sigma..sup.2.sub.RSS, the received signal strength difference is
subject to noise with variance 2.sigma..sup.2.sub.RSS. This means
that with known antenna information, it is possible to match a
reported received signal strength difference to a direction of
departure corresponding to the reported difference. See
PCT/SE2011/051226 for further details.
Estimating Velocity Using Doppler Estimation:
[0284] If the mobile is moving at a velocity v relative to the
serving base station, the base station receiver will observe a
shift in carrier frequency f.sub.c, such that the received
frequency f.sub.r is either lower (mobile is moving away from the
base station) or higher (mobile is moving towards the base station)
than the carrier frequency. The differences can be used to estimate
the relative velocity v with respect to the base station:
f r = 1 1 + v c f c . ##EQU00004##
[0285] More details can be found in U.S. Pat. No. 6,873,852, which
is incorporated here by reference.
* * * * *